The present invention relates to a device for regulating the flow in a siphon tube assembly. More particularly, it relates to a device fitted to the outlet end of a drainage siphon tube, allowing it to function continuously, or intermittently, with an overflow superior to a defined minimal critical outflow determined by on-site parameters.
In my earlier patent, U.S. Pat. No. 4,717,284, I disclose a device for draining soils in depth, the subject matter of which is incorporated herein.
French Patent No. 2,593,203 and European Patent Application No. EP 0 230 918 disclose a drainage siphon device capable of functioning continuously, and in an autonomous way, without the risk of unpriming, as a result of which there is no need for repeated care or systematic surveillance. While satisfactory in the great majority of situations encountered in the field, it happens, however, that the functioning of this device is, under certain circumstances, problematic where the water to be siphoned comprises a significant amount of dissolved gases. When the water rises within the tube forming the siphon, its pressure decreases and part of the gas is freed in the form of bubbles. These bubbles are drawn along the water flow as long as the latter remains adequately strong. However, below a certain minimum outflow, called a "critical point" the bubbles are no longer drawn along but instead they all rise to the highest point of the siphon, meet there and form a large bubble by coalescence.
Tubes of interior diameter superior to the 10 mm and those whose interior diameter is less than 6 mm present noticeably different behaviors.
In the last case (6 mm and less) when the critical point is reached, the bubbles take up or occupy the entire cross section of the siphon tube, as a result of which outflow is stopped. At the same time, the continuous feed flow from the borehole in which the drain is placed results in an increase in the water level within the drain and thus, an increase in the hydrostatic pressure. This increased pressure reaches a point where it is strong enough to completely eject the large bubble which has accumulated at the highest point, following which the siphon tube works normally again until it enters a new "stopping phase", caused by reaching the "critical point" again and the formation of another bubble.
For tubes of a diameter larger than approximately 10 mm, the bubble stagnating at the highest point of the siphon tube does not at first, take up the whole cross-section of the tube and allows for a certain time a certain outflow until, by coalescence, it also is large enough to totally stop the outflow. Here too, the hydrostatic pressure increases in the borehole until it is strong enough to eject the bubble and allow the outflow to resume. However, the pressure necessary to eject the bubble can, in certain situations be unacceptable or at least undesirable. As discussed in the above patents, this problem can be solved by equipping the drain with several siphon tubes of different diameters, working simultaneously or in turn, according to temporary conditions. However, this solution requires fittings which can be costly, cumbersome and complicated due to the several siphon tubes involved.